Gas compressor and method with improved valve assemblies

ABSTRACT

A gas compressor and method according to which a piston assembly reciprocates in a bore to draw the fluid to be compressed into the bore during movement of the piston unit in one direction and to compress the fluid during movement of the piston unit in the other direction.

BACKGROUND

[0001] This invention relates, in general, to a fluid compressor, and,more particularly, to a compressor having improved discharge valves.

[0002] Many reciprocating compressor cylinders utilize a piston assemblythat reciprocates in a cylinder formed in the compressor body, withouter heads closing off the ends of the cylinder. In these arrangements,the piston assembly often includes a discharge valve that controls thegas flow through its body structure into the cylinder and thencompresses the fluid before permitting the compressed fluid to dischargethrough the outlet.

[0003] These type of valve assemblies utilize a plate valve which“lifts” off a valve seat in response to a pressure differential createdfrom one side of the valve to the other side, to permit flow through theassembly. However, this flow area through the valve assembly is oftenlimited in size, which compromises the efficiency of the compressor.

[0004] Therefore, what is needed is a compressor of the above typeaccording to which the valve assemblies have a relatively large flowarea and the compressor thus has an increased efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a partial sectional-partial elevational, view of a fluidcompressor according to an embodiment of the present invention.

[0006]FIG. 2 is an enlarged sectional view of the piston assemblies ofthe compressor of FIG. 1.

[0007]FIG. 3 is an exploded, isometric view of an outboard valveassembly utilized in a piston assembly of FIG. 2.

[0008]FIG. 4 is an exploded, isometric view of an inboard valve assemblyutilized in the piston assembly of FIG. 2.

[0009]FIGS. 5a-5 h are diagrammatic views depicting the operation of thecompressor of FIG. 1.

DETAILED DESCRIPTION

[0010] Referring to FIG. 1 of the drawings the reference numeral 10refers, in general, to a compressor for compressing a fluid, such asgas, according to an embodiment of the present invention. The compressor10 includes a cylindrical housing 12 defining an internal cylindricalbore 14 and a radially extending outlet 15 that registers with the bore14.

[0011] An outer head 16 is formed at one end of the housing 12, and aframe head 18 is mounted at the other end of the housing. A plurality ofinlet chambers are formed through the head 16 with two being shown inFIG. 1 and referred to by the reference numerals 16 a and 16 b. Theinlet chambers 16 a and 16 b, as well as the other inlet chambers in thehead 16, are interconnected and are in fluid communication with an inletconduit 20 formed on the body member 12.

[0012] The head 18 is identical to the head 16 and, as such, has aplurality of inlet chambers formed therein, two of which are shown inFIG. 1 and referred to by the reference numerals 18 a and 18 b. Theinlet chambers 18 a and 18 b, as well as the other inlet chambers in thehead 18, are interconnected and are in fluid communication with an inletconduit 22 formed on the body member 12.

[0013] The inlet conduits 20 and 22 are adapted to receive a fluid to becompressed, such as a gas, and direct the gas into the heads 16 and 18for discharge into the bore 14 as shown by the arrows in FIG. 1.

[0014] A drive rod 24 extends through the center of the head 18 and intothe bore 14, and is mounted for reciprocal movement in a packing glandassembly 26 mounted in a chamber formed in the head 18. The packinggland assembly 26 functions in a conventional manner to seal againstcompressed gas from leaking past the rod 24. An end portion of the rod24 projects from the bore 14 and through a collar 27 mounted to the faceof the head 18 and, although not shown in the drawings, it is understoodthat it is connected to a conventional prime mover for reciprocating therod in a right-to-left and in a left-to-right direction as viewed inFIG. 1, as shown by the double-headed arrow.

[0015] An outboard piston assembly 30 and an inboard piston assembly 32are disposed in the bore 14 in a spaced relation. The rod extendsthrough central openings in the piston assemblies 30 and 32, and a jamnut 34 abuts the outboard face of the piston assembly 30 and isconnected to the other end of the rod 24 in any conventional manner,such as by a plurality of bolts, or the like. A tubular spacer 36extends between the piston assemblies 30 and 32 and is connected theretoin a manner to be described. Thus, when the above-mentioned reciprocalmovement is imparted to the rod 24, the piston assemblies 30 and 32reciprocate in the bore 14 with the rod 24, and function to draw the gasinto the bore 14 and compress the gas before the gas is dischargedthrough the outlet 15, in a manner to be described.

[0016] As shown in FIG. 2, the outboard piston assembly 30 consists ofan outboard valve assembly 40 and an inboard valve assembly 42 disposedin an abutting relationship. The jam nut 34 abuts the outboard face ofthe outboard valve assembly 40, the inboard face of the outboard valveassembly abuts the outboard face of the inboard valve assembly 42 , andthe inboard face of the inboard valve assembly is connected to thespacer 34.

[0017] The outboard valve assembly 40 is shown in detail in FIGS. 2 and3 and consists of an annular valve seat 46 having an outer diameter lessthat the diameter of the inner wall of the body member 12 defining thebore 14. A plurality of spaced bores 46 a (FIG. 2) extend from theoutboard face of the valve seat to a plurality of angularly and radiallyspaced, slots 46 b (FIG. 3) formed in the inboard face of the seat. Areduced-diameter, annular stop 46 c extends from the inboard face of theseat 46 and a relatively large central opening 46 d is formed throughthe seat 46 for receiving the rod 24 (FIG. 2).

[0018] An annular valve plate 48, having a diameter slightly less thanthe diameter of the valve seat 46, is provided and has a plurality ofangularly and radially spaced, arcuate slots 48 a formed therethrough. Arelatively large central opening 48 b is formed through the valve plate48 for receiving the rod 24 (FIG. 2). The valve plate 48 is adapted tomove axially in the bore 14 relative to the valve seat 46 between afirst position in which it engages the inboard face of the valve seat 46and a second position in which it is spaced from the seat. In the firstposition, the non-slotted portion of the valve plate 48 blocks the slots46 b of the valve seat 46 to prevent gas flow through the valve seat,and in the second position gas can flow through the slots 46 b andthrough the slots 48 a of the valve plate.

[0019] An annular dampening plate 50 is disposed adjacent the valveplate 48, is approximately the same diameter as the valve plate, andfunctions to decelerate movement of the valve plate under conditions tobe described to prevent damage caused by impact inertia. To this end,the mass of the dampening plate 50 is normally greater than that of thevalve plate 48 so that the plate 50 dampens movement of the plate 48under conditions to be described. A plurality of angularly and radiallyspaced, arcuate slots 50 a extend through the plate 50 and are inalignment with the slots 48 a of the plate 48. Six angularly-spacedthrough openings 50 b are also provided in the plate 50 for reasons tobe described, and a relatively large central opening 50 c is formedthrough the plate 50 for receiving the rod 24 (FIG. 2).

[0020] A valve guard 52 is disposed adjacent the dampening plate 50 andfunctions to provide a positive stopping point for the dampening plate50, also under conditions to be described. The valve guard 52 consistsof a housing 54 having a tapered, or funnel-shaped, cross-section. Aplate 56 is disposed in the housing 54 and has a plurality of throughopenings 56 a and a relatively large central through opening 56 b forreceiving the rod 24. As shown in FIG. 2, the outboard end portion ofthe housing 54 envelopes the outer circumferential portions of the valveplate 48 and the dampening plate 50.

[0021] One end portion of a spring 58 extends into a pocket, or thelike, (not shown) formed in the outboard face of the valve guard 52. Thespring 58 extends through an opening 50 b in the dampening plate 50 andits other end engages the inboard face of the valve plate 48. Althoughonly one spring 58 is shown, it is understood that five other springsare provided which are identical to the spring 58 and which extendthrough the remaining five openings 50 b in the plate 50, respectively.The springs 58 function to urge the valve plate 48 into engagement withthe valve seat 46 until forced away from the seat by differential fluidpressure, as will be described.

[0022] One end of a spring 60 also extends into a pocket, or the like,(not shown) formed in the outboard face of the valve guard 52 and itsother end engages the inboard face of the dampening plate 50. The spring60 functions to urge the dampening plate 50 into engagement with thestop 46 c and in a slightly spaced relation to the valve plate 48 untilforced away from the stop by differential fluid pressure. Although onlyone spring 60 is shown in the drawing, it is understood that additionalsprings can be provided that are identical to the spring 60 and functionin the same manner.

[0023] The springs 58 and 60 normally bias the valve plate 48 into asealing position against the valve seat 46, and the dampening plate 50against the stop 46 c, respectively.

[0024] An alignment pin 62 extends though corresponding aligned openingsin the valve plate 48 and the dampening plate 50 for maintaining properangular alignment of the plates. Two cap screws 64 a and 64 b extendthrough aligned openings in the valve seat 46, through the centeropenings 48 b and 50 c in the plates 48 and 50, respectively, and engagethreaded bores in the valve guard 52 to maintain the valve assembly 40in its assembled condition shown in FIG. 2.

[0025] The inboard valve assembly 42 is shown in detail in FIGS. 2 and 4and consists of an annular valve seat 66 having an outer diameterslightly less that the diameter of the inner wall of the body member 12(FIG. 1) defining the bore 14. A plurality of spaced bores 66 a (FIG. 2)extend from the outboard face of the valve seat 66 to a plurality ofradially spaced, slots 66 b (FIG. 3) formed in the inboard face of theseat. A plurality of angularly-spaced portals 66 c are formed though theseat 66, and a reduced-diameter annular stop 66 d projects from theinboard face of the valve seat 66.

[0026] A plurality of circumferential grooves 66 e are formed in theouter surface of seat 66 and receive a corresponding number of sealrings 67 which engage the inner wall of the body member defining thebore 14, to seal against the flow of compressed gas from the bore. Arelatively large central opening 66 f is formed through the seat 46 forreceiving the rod 24 (FIG. 2).

[0027] An annular valve plate 68, is provided and has a plurality ofangularly and radially spaced, arcuate slots 68 a extendingtherethrough. The valve plate 68 is adapted to move in the bore 14between a first position in which it engages the inboard face of thevalve seat 66, with the non-slotted portion of the plate blocking theslots 66 b of the valve seat, and a second position in which it isspaced from the seat to permit the flow of gas through the slots in thevalve seat and the slots 68 a of the valve plate. A plurality ofangularly-spaced portals 68 b are formed though the plate 68, and arelatively large central opening 68 c is formed through the plate 68 forreceiving the rod 24 (FIG. 2).

[0028] An annular dampening plate 70 is disposed adjacent the valveplate 68 and functions to decelerate the valve plate under conditions tobe described to prevent damage caused by impact inertia. To this end,the mass of the dampening plate 70 is greater than that of the valveplate 68 so that the plate 70 dampens movement of the plate 68. Aplurality of angularly and radially spaced, arcuate slots 70 a, and aplurality of angularly spaced portals 70 b extend through the plate 70.The slots 70 a register with the slots 68 a of the valve plate 68, andthe portals 70 b register with the portals 68 b of the valve plate 68.Six angularly-spaced openings 70 c are provided through the plate 70 forreasons to be described, and a relatively large central opening 70 d isformed through the plate 70 for receiving the rod 24 (FIG. 2).

[0029] An annular guard plate 72 is disposed adjacent the dampeningplate 70 and functions to provide a positive stopping point for thedampening plate 70, also under conditions to be described. A pluralityof angularly-spaced portals 72 a extend through the guard plate 72 andregister with the portals 70 b of the dampening plate 70, and arelatively large central opening 72 b is formed through the guard plate72 for receiving the rod 24 (FIG. 2). The plate 72 also has a pluralityof relatively small through openings 72 c, for reasons to be described.

[0030] One end portion of a spring 74 extends into a pocket, or thelike, (not shown) formed in the outboard face of the guard plate 72. Thespring 74 extends through an opening 70 c in the dampening plate 70 andits other end engages the inboard face of the valve plate 68. Althoughonly one spring 74 is shown, it is understood that five other springsare provided which are identical to the spring 74 and which extendthrough the remaining five openings 70 c, respectively. The springs 74function to urge the valve plate 68 into engagement with the valve seat66 until forced away from the seat by differential fluid pressure underconditions to be described.

[0031] One end of a spring 76 also extends into a pocket, or the like,(not shown) formed in the outboard face of the valve guard 72 and itsother end engages the inboard face of the dampening plate 70 to urge thedampening plate into engagement with the stop 66 d until forced away bydifferential fluid pressure. Although only one spring 76 is shown in thedrawing, it is understood that additional springs can be provided thatare identical to the springs 74 and 76 and function in the same manner.

[0032] An alignment pin 78 extends though corresponding aligned openingsin the dampening plate 70 and the valve plate 68 for maintaining properangular alignment of the plates. Two cap screws 80 a and 80 b extendthrough aligned openings in the valve seat 66, through the centeropenings in the plates 68 and 70, though the valve guard 72 and engagethreaded bores in the spacer 24 (FIG. 2) to maintain the valve assembly42 in its assembled condition shown in FIG. 2.

[0033] As shown in FIG. 2, the outer diameter of the valve assembly 40is considerably less than the outer diameter of the valve assembly 42and the corresponding inner wall of the body member 12 defining the bore14. Thus, some of the gas from the head 16 passes around the outersurfaces of the valve assembly 40 and directly to the valve assembly 42under conditions to be described.

[0034] The general operation of the valve assemblies 40 and 42 is asfollows. When gas is admitted into the head 16 from the inlet conduit20, the gas passes through the inlet chambers in the head, including thechambers 16 a and 16 b, and into the outboard end portion of the bore14. As better shown in FIG. 1, a portion of this gas passes around theouter surface of the valve assembly 40 of the piston assembly 30 and tothe valve assembly 42 which controls the flow of the gas in a manner tobe described.

[0035] As better shown in FIGS. 2 and 3, the remaining portion of thegas passes through the bores 46 a and the slots 46 b in the valve seat46 and exerts a pressure against the outboard face of the valve plate48. When this pressure exceeds the pressure acting on the inboard faceof the valve seat 46 by the springs 58, the valve plate 48 will beforced off the seating surface of the valve seat 46 and will move in aleft-to-right direction as viewed in FIG. 2 until it encounters thedampening plate 50, and both plates then travel a short distance inunison until they come in contact with the plate 56 of the valve guard52.

[0036] This allows the passage of compressed gas through the openings 46a and the slots 46 b in the valve seat 48, and through the aligned slots48 a and 50 a in the valve plate 48 and the dampening plate 50,respectively, before passing through the openings 56 a in the plate 56.The tapered housing 54 of the valve guard functions to funnel, or directthe gas passing through the openings 56 a towards the center, or axis ofthe valve assembly 42 so that the gas passes through the aligned portals66 c, 68 b, 70 b, and 72 a (FIG. 4) of the valve seat 66, the valveplate 68, the dampening plate 70, and the guard plate 72, respectively,before the gas enters that portion of the bore 14 disposed between thepiston assemblies 30 and 32 as shown in FIG. 1.

[0037] The above-mentioned gas from the head 16 that passed around theouter surface of the valve assembly 40 of the piston assembly 30 passesdirectly to the valve assembly 42. As better shown in FIGS. 2 and 4,this latter gas then passes through the bores 66 a and the slots 66 b inthe valve seat 66 and exerts a pressure against the outboard face of thevalve plate 68. When this pressure exceeds the pressure acting on theinboard face of the valve seat 66 by the springs 74, the valve plate 68will be forced off the seating surface of the valve seat 66 and moved ina left-to-right direction, as viewed in FIG. 2. This allows passage ofcompressed gas through the valve seat 66 and through the aligned slotsin the valve plate 68, the dampening plate 70 and the valve guard 72before the gas enters the portion of the bore 14 extending between thepiston assemblies 30 and 32. Thus, this portion of the bore 14 receivestwo streams of gas from the piston assembly 30, one that flows throughboth valve assemblies 40 and 42, and one that flows only through thevalve assembly 42.

[0038] During the above operation, and as a non-limitative example, thevalve plates 48 and 68 will move, or “lift”, for approximately 0.060″until they come into contact with their corresponding dampening plates50 and 70, respectively. The plates 48 and 50, as well as the plates 68and 70, will then move together approximately another 0.020″ while theydecelerate and then come into contact with their respective valve guards52 and 72.

[0039] Referring to FIG. 2, the piston assembly 32 consists of twoabutting valve assemblies 86 and 88 that are identical to the valveassemblies 40 and 42, respectively, of the piston assembly 30. The valveassemblies 86 and 88 face in the opposite direction than the valveassemblies 40 and 42 and the valve assembly 86 is positioned inboard ofthe valve assembly 88. The valve assemblies 86 function in a manneridentical to the functions of the valve assemblies 40 and 42,respectively. Thus, some of the fluid introduced into the bore 14 fromthe inlet chambers formed in the head 18, including the inlet chambers18 a and 18 b, will pass into end portion of the bore 14 inboard of thevalve assembly 86. When the rod 24, and therefore the valve assemblies30 and 32, move in a left-to-right direction, the pressure of the lattergas will exert a pressure on the valve plate associated with the valveassembly 86 to force it to move in a right-to-left position from itssealing position before the gas passes through the valve assembly 88 andinto that portion of the bore between the piston assemblies 30 and 32.

[0040] The remaining portion of the gas from the head 18 will passaround the outer surfaces of the valve assembly 86 and directly to thevalve assembly 88. This latter gas will exert a pressure on the valveplate associated with the valve assembly 88 to force it to move in aright-to-left position from its sealing position before the gas passesthrough the valve assembly 88 and into the latter portion of the bore14. Thus, the bore 14 also receives two streams of gas from the pistonassembly 32, one that flows through both valve assemblies 86 and 88, andone that flows only through the valve assembly 88.

[0041] The complete operation of the compressor 10 will be described inconnection with FIGS. 5A-5H. As shown in FIG. 5A, the piston assemblies30 and 32 divide the bore 14 into a section 14 a between the head 16 andthe piston assembly 30, a section 14 b between the piston assemblies 30and 32, and a section 14 c between the piston assembly 32 and the head18. For the purposes of example, it will be assumed that, as a result ofa previous cycle of operation, a fluid, such as gas, or other product,has been drawn into the bore section 14 a, and the rod 24, and thereforethe piston assemblies 30 and 32, are in their extreme right position, asviewed in FIG. 5a as a result of a previous cycle of the operation.

[0042] The gas is introduced, via the inlet conduit 22, into the inletchambers, including the chambers 18 a and 18 b, formed in the head 18.The rod 24, and therefore the piston assemblies 30 and 32, are moved ina right-to-left direction, as shown by the solid arrow, from theposition of FIG. 5A to the position of FIG. 5B, under the power of theabove-mentioned prime mover. This movement draws gas from the head 18into the bore section 14 c and causes the gas that is present in thebore section 14 a from the previous cycle to be compressed.

[0043] Further right-to-left movement of the rod 24, and therefore thepiston assemblies 30 and 32, to the position of FIG. 5C causesadditional gas to be drawn in the bore section 14 c in the mannerdiscussed above, and further increases the fluid pressure in the boresection 14 a. Some of this compressed gas flows into the valve assembly40 of the piston assembly 30 in the manner described above, and theright-to-left movement of the rod 24 continues until the pressure in thebore section 14 a is great enough to move the valve plate 48 of thevalve assembly 40 in a left-to-right direction off of its valve seat 46.The above portion of the compressed gas thus flows through the valveassembly 40 in the manner described above and to the valve assembly 42where it passes through the aligned openings 66 c, 68 b, 70 b, and 72 a(FIG. 4) of the latter assembly and to the bore section 14 b, as shownby the hollow arrows in FIG. 5C. Thus, in this case the valving functionof the valve seat 66 and the plate 68 are bypassed.

[0044] The other portion of the compressed gas in the bore section 14 apasses around the valve assembly 40 and directly into the valve assembly42 as also described above. When the gas pressure in the bore section 14a is great enough to move the valve plate 68 of the valve assembly 42 ina left-to-right direction off of its valve seat 46, the latter portionof the compressed gas thus flows through the valve assembly 42 in themanner described above and into the bore section 14 c.

[0045] The compressed gas that flows into the bore section 14 b in thetwo manners described above exits the body member 12 through the outlet15 and is transferred from the compressor 10 via a pipe, or the like,connected to the outlet.

[0046] This right-to-left movement of the rod 24 and the pistonassemblies 30 and 32 continues, causing further compression of the gasin the bore section 14 a and passage of the compressed gas though thevalve assemblies 40 and 42 of the piston assembly 30. The gas in thebore section 14 a discharges through the outlet 15 as described aboveuntil the rod 24 and the piston assemblies 30 and 32 reach the endposition shown in FIG. 5D.

[0047] Referring to FIG. 5E, gas is introduced, via the inlet conduit 20into the inlet chambers, including the chambers 16 a and 16 b, formed inthe head 16. The rod 24, and therefore the piston assemblies 30 and 32,are moved in a left-to-right direction, as shown by the solid arrow,from the position of FIG. 5E to the position of FIG. 5F, under the powerof the above-mentioned prime mover. This movement draws gas from thehead 16 into the bore section 14 a and causes the gas that is present inthe bore section 14 c as a result of the above operation to becompressed.

[0048] Further left-to-right movement of the rod 24, and therefore thepiston assemblies 30 and 32, to the position of FIG. 5G causesadditional gas to be drawn in the bore section 14 a in the mannerdiscussed above, and further increases the fluid pressure in the boresection 14 c. Some of this compressed gas flows into the valve assembly86 of the piston assembly 30 in the manner described above, and theleft-to-right movement of the rod 24 continues until the pressure in thebore section 14 c is great enough to move the valve plate of the valveassembly 86 in a right-to-left direction off of its valve seat. Theabove portion of the compressed gas thus flows through the valveassembly 86 in the manner described above and to the valve assembly 88where it passes through the aligned openings of the latter assembly andto the bore section 14 b, as shown by the hollow arrows in FIG. 5G.

[0049] The other portion of the compressed gas in the bore section 14 cpasses by the valve assembly 86 and directly into the valve assembly 88as also described above. When the gas pressure in the bore section 14 cis great enough to move the valve plate of the valve assembly 88 in aright-to-left direction off of its valve seat 46, the latter portion ofthe compressed gas thus flows through the valve assembly 88 in themanner described above.

[0050] The compressed gas that flows into the bore section 14 b in thetwo manners described above exits the body member 12 through the outlet15 and is transferred from the compressor 10 via a pipe, or the like,connected to the outlet.

[0051] This right-to-left movement of the rod 24, and the pistonassemblies 30 and 32, continues, causing further compression of the gasin the bore section 14 c and passage of the compressed gas though thepiston assembly 32 and discharge of the gas through the outlet 15 asdescribed above until the rod 24 and the piston assemblies reach the endposition shown in FIG. 5H.

[0052] The above cycle is then repeated and the compressor 10 thusfunctions to continuously receive gas via the inlet conduits 20 and 22and discharge compressed gas from the outlet 15.

Alternatives and Equivalents

[0053] It is understood that some of the components of the compressor 10have been omitted in the interest of clarity. For example, although adual acting system having two piston assemblies is disclosed above, itis understood that the present invention is equally applicable to asingle acting system assembly in which only one piston assembly would beprovided which would function in an identical manner to the pistonassemblies 30 and 32. Further, the present invention is not limited tothe particular design of the valve assemblies 40, 42, 86 and 88disclosed above, but rather other types of valve assemblies can be used,such as, for example, those disclosed in U.S. Pat. No. 5,011,383 or U.S.Pat. No. 5,015158 (the disclosures of which are incorporated byreference) or those employing a series of rings or bullets. Stillfurther, a plurality of inlet valves can be disposed in the inletchambers defined in the heads 16 and 18 as disclosed in co-pending U.S.application Ser. No. ______ (attorney's docket no 26333.11) thedisclosure of which is incorporated by reference. Moreover, anotherfluid, other than gas, can be compressed by the compressor 10. Moreover,the number of openings extending through the valve seat 66, the plates68 and 70, and the valve guard 72 can be varied; and the number ofsprings 58, 60, 74, and 76 utilized in the above manner can be varieddepending on the particular load conditions.

[0054] Those skilled in the art will readily appreciate that many othermodifications are possible in the exemplary embodiments withoutmaterially departing from the novel teachings and advantages of thisinvention. Accordingly, all such modifications are intended to beincluded within the scope of this invention as defined in the followingclaims. In the claims, means-plus-function function clauses are intendedto cover the structures described herein as performing the recitedfunction and not only structural equivalents, but also equivalentstructures.

What is claimed is:
 1. A fluid compressor comprising a body memberhaving an inlet and an outlet and defining an internal bore, a firstvalve assembly disposed in the bore, a second valve assembly disposed inthe bore in an axially spaced relation to the first valve assembly,means for moving the valve assemblies in a first direction in the boreto draw fluid from the inlet into the bore so that a first portion ofthe fluid is directed to the first valve assembly and a second portionof the fluid is directed to the second valve assembly, the means adaptedto move the valve assemblies in a second direction in the bore toincrease the fluid pressure in the bore, the first valve assembly beingresponsive to a predetermined fluid pressure acting on it for permittingthe flow of the first portion of fluid through it and to the secondvalve assembly, the second valve assembly defining a bypass passage forreceiving the first portion of fluid from the first valve assembly andpassing it to the bore for passage to the outlet, the second valveassembly being responsive to the other portion of fluid exerting apredetermined fluid pressure on it for permitting the flow of fluidthrough it and to the bore for passage to the outlet.
 2. The compressorof claim 1 wherein the second direction is opposite to the firstdirection.
 3. The compressor of claim 1 wherein the means comprises arod mounted for reciprocal movement in the bore and wherein the valveassemblies are attached to the rod for reciprocation therewith
 4. Thecompressor of claim 1 wherein the fluid passes from the inlet into oneend portion of the bore and wherein the valve assemblies are locatedbetween the latter end portion of the bore and the outlet.
 5. Thecompressor of claim 4 wherein another inlet is disposed in the bodymember for introducing additional fluid into the other end of the bore,and further comprising a third valve assembly disposed in the bore in anaxially spaced relation to the second valve assembly, a fourth valveassembly disposed in the bore in an axially spaced relation to the thirdvalve assembly, the means also moving the third and fourth valveassemblies in the first and second directions, whereby movement of thevalve assemblies in the second direction draws the additional fluid fromthe other inlet into the other end portion of the bore so that a firstportion of the additional fluid is directed to the fourth valve assemblyand a second portion of the additional fluid is directed to the thirdvalve assembly, wherein movement of the valve assemblies in the firstdirection increases the fluid pressure in the other end portion of thebore, the fourth valve assembly being responsive to a predeterminedfluid pressure acting on it for permitting the flow of the first portionof the additional fluid through it and to the third valve assembly, andthe third valve assembly defining a bypass passage for receiving thefirst portion of the additional fluid from the fourth valve assembly andpassing it to the bore for passage to the outlet, the third valveassembly being responsive to the other portion of fluid exerting apredetermined fluid pressure on it for permitting the flow of fluidthrough it and to the bore for passage to the outlet.
 6. The compressorof claim 5 wherein the second direction is opposite to the firstdirection.
 7. The compressor of claim 5 wherein the means comprises arod mounted for reciprocal movement in the bore and wherein the valveassemblies are attached to the rod for reciprocation therewith
 8. Afluid compressor comprising a body member defining an internal bore, aninlet registering with the bore for receiving the fluid to becompressed, and an outlet registering with the bore; at least one pistonassembly mounted for reciprocal movement in the bore between the inletand the outlet and comprising two valve assemblies arranged so thatmovement of the piston assembly in one direction in the bore draws thefluid from the inlet into the bore and movement of the piston assemblyin the opposite direction increases the fluid pressure in the bore, andso that a first portion of the fluid is directed to one of the valveassemblies and another portion of the fluid is directed to the othervalve assembly; the one valve assembly normally preventing the flow ofthe first portion of fluid but being responsive to a predetermined fluidpressure acting on it for permitting the flow of the first portion offluid through it and to the other valve assembly, and the other valveassembly defining a bypass passage for receiving the first portion offluid from the first valve assembly and passing it to the bore forpassage to the outlet, the other valve assembly being responsive to theother portion of fluid exerting a predetermined fluid pressure on it forpermitting the flow of fluid through it and to the bore for passage tothe outlet.
 9. The compressor of claim 8 wherein there are two pistonassemblies mounted for reciprocal movement in the bore.
 10. Thecompressor of claim 8 wherein the second direction is opposite to thefirst direction.
 11. The compressor of claim 8 further comprising a rodmounted for reciprocal movement in the bore and connection to the pistonassemblies so that the piston assemblies reciprocate with the rod. 12.The compressor of claim 8 wherein the fluid passes from the inlet intoone end portion of the bore and wherein the valve assemblies are locatedbetween the latter end portion of the bore and the outlet.
 13. A methodfor compressing a fluid, comprising reciprocating two valve assembliesin a bore, drawing fluid into the bore in response to movement of thevalve assemblies in a first direction in the bore, directing a firstportion of the fluid to one of the valve assemblies, directing anotherportion of the fluid to the other valve assembly, increasing thepressure in the bore in response to movement of the valve assemblies ina second direction, permitting the flow of fluid through the one valveassembly and to the other valve assembly in response to a predeterminedfluid pressure acting on the one valve assembly, the first portion offluid bypassing the other valve assembly and passing to the outlet, andpermitting the flow of the other portion of the fluid the other valveassembly and to the outlet in response to a predetermined fluid pressureacting on the other valve assembly.
 14. The compressor of claim 13wherein the second direction is opposite to the first direction.
 15. Thecompressor of claim 13 further comprising reciprocating a rod in thebore, and connecting the valve assemblies to the rod for reciprocationtherewith
 16. The compressor of claim 13 wherein the fluid passes fromthe inlet into one end portion of the bore and wherein the valveassemblies are located between the latter end portion of the bore andthe outlet.